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Riverside erosion is one of the most dangerous hazards that are happening in the lower Mekong River in the last two decades. Many of ancient towns such as Tanchau, Hongngu, Sadec and populated cities like Longxuyen, Cantho have being suffered from this problem. Erosion has taken away hundreds of hectares of farming land; damaged many wards, schools, hospitals, offices, and transportation structures as bridges, ferries and main roads. Annually, it causes averagely in these areas in excess of USD 1.0 million. In addition, many people were killed in the last years for example 30 people in Tanchau (1988) and Hongngu (1992). The study, based on interpretation of satellite images and monitoring of channel cross-sections using echo-sounder, has identified the rate of bank erosion in three grades: 5-10m/year (Cantho), 10-30m/year (Sadec, Longxuyen), and >30m/year (Tanchau, Hongngu). The eroded shorelines in every area have been stretched from 6 km to 10 km. These occur at sites where direction of the stream suddenly changes or where branches of river are confluent.
The main factors causing the riverside erosion consist of: high velocity flow, loose sediments, meandering of the Mekong River in the flood plain and over-loading capacity of anthropogenic structures. Among these factors, meandering movement is the most reasonable one leading to the hazard of riverside erosion along the Mekong River.
Moreover, these affected areas are among the economical development centers in the South Western of Vietnam. There are also many valuable cultural heritages and French architectures. Therefore, the protection and planning to minimize losses from erosion are highly recommended to the government at various levels.
Keywords: Erosion hazard; Channel change; Environmental geology, Mekong delta
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